N-Doped Yellow TiO2 Hollow Sphere-Mediated Visible-Light-Driven Efficient Esterification of Alcohol and N-Hydroxyimides to Active Esters

Herein we report a simple synthetic protocol for N-doped yellow TiO2 (N-TiO2) hollow spheres as an efficient visible-light-active photocatalyst using aqueous titanium peroxocarbonate complex (TPCC) solution as precursor and NH4OH. In the developed strategy, the ammonium ion of TPCC and NH4OH acts as nitrogen source and structure-directing agent. The synthesized N-TiO2 hollow spheres are capable of promoting the synthesis of active esters of N-hydroxyimide and alcohol through simultaneous selective oxidation of alcohol to aldehyde followed by cross-dehydrogenative coupling (CDC) under ambient conditions upon irradiation of visible light. It is possible to develop a novel and cost-effective one-pot strategy for the synthesis of important esters and amides on gram scale using the developed strategy. The catalytic activity of N-TiO2 hollow spheres is much superior to that of other reported N-TiO2 samples as well as TiO2 with varying morphology.